Displays play an important role in everyday life. The displays have been widely used in the fields such as TV, desk-top computers, notebook computers, tablets, mobile devices, biomedicine, industry and traffics. Examples of the displays include CRT display, liquid crystal display, OLED display, plasma display and the like, wherein the liquid crystal display is the most popular display. In comparison to the conventional CRT display, the liquid crystal display has benefits of smaller volume, lighter weight, lower radiation, lower power consumption, and so on. Until now, the displays are continuously improved.